This invention relates to a method and system to control the level of a liquid in a pressurised vessel or at least in a reservoir in which a pressure difference exists between the fluid above the liquid whose level is being controlled and an outflow of the liquid from the reservoir. This invention finds particular application in a fluid separation system to separate immiscible fluids of different density. The invention also relates to an improved fluidic valve.
In the petroleum extraction industry, but also elsewhere, there is frequently a requirement to separate different density immiscible fluids such as oil and water or oil and gas or all three. Indeed such mixtures may be found in large volumes and often in rapidly varying ratios of one component with respect to the other. A major problem associated with such multiphase flow is the fact that the constituent parts of the flow are extracted at a variable rate, such that in operation there is poor control over, for example, the amount of gas followed by the amount of liquid obtained from the well. This sometimes results in what is known as xe2x80x9cslugging flowxe2x80x9d, which can cause control problems.
Partial processing is a system where coarse separation of the various components is effected adjacent a well site, or other location near where the mixed components requiring separation first emanate. This results in much reduced transportation costs. In the petroleum extraction industry, for example, water and oil are frequently combined products of an oil well, and while the oil is to be recovered and transported to a refinery, the water is to be reused for pressurising the well. Consequently, to transport the water to a refinery and then back to the well is wasteful.
However, separation is not straightforward. As mentioned above, there are wide variations in the ratio of one component with respect to the other. Secondly, there is frequently solid matter entrained in the flow, which also need separation and isolation. Thirdly, the separation may need to be performed sub-sea, or in a remote site, where system reliability becomes of paramount importance. Gravitational separation in a vessel is possible, using a weir system for example, but maintaining the different levels of the components in the vessel is problematic when widely varying in-flow of the components occurs. Then, it is necessary to control the outflow of the components so that an appropriate interface level between the components is maintained. However, a simple weir system to maintain a level cannot function if there is a pressure difference between the less dense fluid and the outflow of the dense fluid. In this event there is the danger that the difference will simply result in forcing of the less dense fluid through the dense fluid outflow.
Pressure variation which the vessel may occur as a result of changes to the inflow rate, or alternatively, from variations to the outflow rate for one or more of the fluids in the system.
It is therefore important to maintain steady-state levels of, for example, oil, gas and water in the vessel so that separation of the fluids can be adequately controlled. Pre-separation of an oil-water steam allows the use of more compact downstream equipment. Further benefits of partial processing include the reduction of bottlenecking in the vessels and an increased yield from new and mature sites.
As mentioned above, another problem associated with production of oil and gas is sediment, which has to be removed from the fluid phase, but poses the added problem of obstructing outlets, and causing wear and stress on the component parts of systems with which is comes into contact.
Fluidic valves are known and have various design possibilities employing vortices or other properties of fluid flow to control flow from an input to an output.
It is known to employ vortex valves, which are commonly referred to as vortex amplifiers, and which comprise a vortex chamber, input and output ports, and a control port. The control port is tangential to the vortex chamber and induces a vortex in the chamber when there is flow through it. The input and output ports are generally arranged axially and/or radially with respect to the vortex chamber, one at least being on the circumference of the vortex chamber so that vortex flow in the chamber interfaces with flow into or from the circumferential port. Where a conical vortex chamber is employed, the input and output can be aligned so that resistance to flow, when there is no control port flow, is minimised.
DE-A-2431112 discloses such a valve employed to control the outflow of flood retention reservoirs. A radial main flow to an axial outflow is controlled by two tangential control ports opposing one another. The first port is supplied with flow when the level of the reservoir rises above a low level, thereby tending to reduce flow through the valve from the radial input to the axial output. The second control port is supplied with flow when the level of the reservoir rises above a high level. In this event, the flows through the control ports cancel one another""s effect and the valve reverts to low resistance. Thus, as the reservoir rises from a minimum level to a maximum level, the valve starts with a low resistance because there is no flow through the control ports. The valve switches to high resistance when the first control port receives a flow as the reservoir level rises above that control port""s input. Finally, the valve switches back to low resistance when the reservoir fills to its maximum level and the other control port is provided with flow as its input is flooded by the rising reservoir level.
However, a problem associated with this arrangement is that the valve is trying to maintain a fixed outflow rate despite changes in the driving hydrostatic head as set by the reservoir level. The valve is not, therefore, suited to level control where a high resistance to flow is required at a low liquid level while low resistance is required at levels above target.
Another problem with the double control vortex amplifier arrangement is that at low liquid levels the vortex chamber can very easily entrain gas and operate partly filled with gas. If the reservoir is pressurized, or suction applied to the outflow, the valve may be prone to the gas venting through one or more of the control ports and this could be highly undesirable in many chemical processing situations.
GB-A-1193089 disclosed a vortex valve having an axially arranged outlet port, two tangential control ports and subsequently no other ports such that inflow to the valve is through the control ports and outflow is through the outlet, the control ports being opposed to one another to reduce any vortex formation when flow occurs through both control ports from a common pressure source.
EP-A-0009335 discloses a T-junction modulator having a divided mainstream flow path to either side of the modulator and two control cylinders to oscillate a control flow across the modulator to inhibit mainstream flow therethrough.
It is therefore an object of the present invention to provide a system in which the level of a liquid in a pressurised chamber can be controlled so that the aforementioned problems are overcome, or at least their effects are mitigated within the design limits of the system.
It is a further object of the invention to provide a fluid separation system incorporating such a level control system.
It is moreover, an object of a different aspect of the present invention to provide a novel form of fluidic valve, suitable for use in level control and/or separation systems in accordance with the present invention or otherwise.
According to the first mentioned objective, the invention therefore provides a pressure vessel containing a reservoir of fluid and having a valve controlling an outlet of the vessel and wherein there is a pressure differential across said valve beyond any hydrostatic pressure head of the reservoir fluid, the vessel comprising a system for the control of the level of reservoir fluid in the reservoir, the system comprising said valve being a fluidic valve and having an outlet port and at least two control ports either or both of which control ports may serve to inlet fluid into the fluidic valve, the inlets being arranged at different levels in the reservoir, whereby the valve has resistance to flow to fluid therethrough which is controlled by flow of said fluid into the control ports, such that said resistance is minimised when flow of fluid in the control ports is substantially equal, and wherein the flow out of the outlet is substantially equal to the combined flow into each control port.
Preferably, said valve is a vortex amplifier comprising a vortex chamber, said control ports being tangential with respect to said chamber and opposed with respect to each other, such that, when the fluid in the reservoir is between said levels, a vortex flow is induced in the vortex chamber increasing its resistance to flow, whereas when the fluid is outside said levels, flow through each control port is substantially the same so that no vortex is established in the vortex chamber whereby the resistance to flow through the valve is minimised.
Preferably, more than two control ports are provided. around said vortex chamber. Moreover, at least two of said control ports may be tangential in the same direction, their inlets in the reservoir being at different levels so that there is gradual switching between maximum and minimum resistances to flow through the valve and vice versa.
The valve may have two axially opposed outlet ports, or may have an adjustable needle-valve disposed in the valve so that it protrudes into the outlet port restricting outflow rate.
Preferably, the valve is arranged such that the pressure in one control port is at least 90%, preferably 95%, and more preferably 99%, of the pressure in the other port.
Alternatively, said valve may comprise a T-junction modulator, wherein a radial diffuser has the narrow end of two conical diffusers, forming said control ports, communicating with said radial diffuser substantially centrally thereof and on opposite sides thereof, said outlet port communicating with a collection gallery around said radial diffuser, whereby absence of supply of fluid to one control port results in oscillation of fluid across said radial diffuser and a high resistance to flow through the valve.
In any event, preferably the control port, whose inlet is nearest the fluid level when both control ports have flow therethrough, is of sufficiently large diameter substantially to eliminate any risk of entrainment of an adjacent fluid in the flow of said reservoir fluid to the valve along said control port.
Preferably, the valve has no other ports than said control and outlet ports. Moreover, the control ports are preferably adapted to permit substantially equal, opposing flows within the vortex chamber to reduce any vortex formation, when said control ports are supplied from a common pressure source. The valve may be located internally of the vessel.
In accordance with the further object of the present invention, said fluid level control system may be employed in a fluid separation system for separating immiscible, different-density fluids, the system comprising a separation vessel with an inlet for said fluids, an outlet for each fluid disposed at different levels in the chamber, and a level control system as defined above, wherein one of said control ports is one of said outlets and the other of said control ports is supplied from the vessel at a level intermediate said outlets, so that a change in level of the boundary between said fluids in the vessel about said intermediate level results in a change in the balance of flow in said control ports to alter the resistance to flow of fluid through the valve.
The fluid level control system may be disposed in a separate level control chamber connected to the separation vessel both above and below the level of the interface between said fluids.
Preferably, in such a separation system, said fluids are a liquid and a gas, the vessel further comprising a second fluidic valve, the first valve controlling outflow of the liquid and the second valve controlling outflow of the gas.
Said first and second valves may have different intermediate levels and each intermediate level may be located between the control ports of the other valve.
There may be three fluids, being two liquids and a gas, in which event, the system may further comprise an intermediate fluidic valve, said first valve being a dense phase valve controlling outflow of the denser of said liquids, said intermediate valve having a supply port intermediate the supply and control ports of the first valve and a control port above the control port of the first valve.
Preferably, the separation system further comprises a shroud around that control port of the or each valve which is nearest said intermediate level when there is balanced flow through both control ports, the shroud being disposed at a level so that only fluid of the same density as the fluid entering the other control port is able to enter the shrouded control port.
The separation vessel may comprise a cyclone separator comprising a substantially circular cylindrical housing whose inlet is tangentially arranged so as to impart swirling flow on the mixed fluids entering the separator.
In one arrangement, a separate level control chamber is provided incorporating a level control system as herein defined, the control chamber being supplied at different levels with gas and liquid partially separated in said cyclone separator.
Preferably, however, the control system is disposed within the cyclone separator, and comprises a substantially circular cylindrical shroud centrally positioned in the cyclone separator so that swirling flow is outside said shroud, the shroud being apertured and one control port of the valve extending up the shroud.
More preferably, however, the level control system is disposed within the cyclone separator, and comprises a control port pipe defining with the wall of the separator an annular control space, swirling flow in the separator being substantially confined to the interior of said pipe and one control port of the fluidic valve being supplied with liquid from inside the pipe, while the other port is supplied with liquid spilling over the pipe and into the annular space. In this event, the annular space may be closed off around part of its circumference to direct flow from the inlet into the interior of the pipe.
The current invention has the capability of handling solids in the fluid phase because fluidic valves have no moving parts which might jam. Moreover, abrasive wear is far less of a problem in fluidic valves than valves with moving parts.
This invention therefore provides a means of controlling the fluid interface in a separator vessel as used for gas/liquid separation with the advantages of:
(i) being able to recover rapidly from xe2x80x9cblow outxe2x80x9d or xe2x80x9cfloodxe2x80x9d conditions in the separator vessel, should that occur;
(ii) substantially eliminating the need to replace damage and worn components because the controlling valve perform their function with no moving mechanical parts; and,
(iii) not requiring any power and operating entirely automatically.
It will also be appreciated that an important aspect of the present invention is its ability to accommodate the contents of the vessel or reservoir being pressurised substantially above the pressure at the outlet of one or more of the valves. Moreover, it is capable of accommodating enhanced gravity systems. In either case the reason is because the arrangement depends primarily on the level of fluid in the reservoir, and not the forces acting on it. The only limitation is the relative pressure above the reservoir with respect to the outside. If this gets too high, blow-out is a possibility and so the system needs to be designed so that, within the design limits of the system, blow-out does not occur.
In accordance with the further aspect of the objectives of the present invention, there is provided a turn-up vortex amplifier, comprising a vortex chamber, one or two axially arranged outlet ports, two or more tangential control ports and substantially no other ports such that inflow to the valve is through the control ports and outflow is through the or each outlet, at least two of the control ports being opposed to one another to reduce any vortex formation when flow occurs through both control ports, and in which an adjustable needle-valve is disposed in the valve so that it protrudes into the outlet port restricting outflow rate.
Such valve preferably has some or all of the features mentioned above in relation to the system aspects of the present invention, which features are applicable to the valve itself.
In a further aspect of the present invention, there is also provided a turn-up vortex amplifier comprising interconnected control, manifold, vortex and outlet plates defining axially arranged inlet control ports, a distribution manifold, a vortex chamber and an axially arranged outlet port respectively.
Preferably, said control plate has a first control port which is centrally arranged, and a plurality of second control ports which are spaced around said central port.
Preferably said vortex plate comprises a plurality of antechambers spaced around said vortex chamber, each with a jet passage tangentially arranged with respect to, and connecting with, the vortex chamber in a direction depending on to which of said first and second control ports said antechambers are connected.
Preferably said manifold plate has a central distribution chamber on one side thereof, which side faces said control plate, radially spaced lumens leading off said distribution chamber and connecting with axial passages communicating with said other side of the manifold plate. Preferably, said manifold plate also has an annular equalisation chamber on said other side, and which is supplied by through-passages communicating one with each of said second control ports.